The production of capsules or sheaths is subject to considerable variation in this species. Thus far coagulated serum has been found the only substrate to stimulate its appearance. It is not known whether the capsular substance is induced by the parasitism. The presence of sheaths within epithelial cells and their absence in cellular exudates suggest the inference that the sheath is a protective substance when the parasite multiplies in living cells. The complete absence of sheaths in some strains might make the recognition of this species difficult, but if its other characters both positive and negative are kept in mind, this difficulty will not be serious.
Next in importance to fluctuations in the presence or absence of capsules is the change in metabolic processes leading to the production and accumulation of fatty substances in the cultures. The original capsular material resembles in its optical characters myelins. In the course of artificial cultivation fat granules make their appearance at the expense of the original myelin-like substance. This process may be regarded as a degenerative one in the sense that it accompanies the gradual loss of the function of secreting the capsular substance.